Since the end of the last century, the virulence of a high-pathogenicity H5 subtype epidemic strain to the waterfowl has been gradually increased, and also has led to the disease and death of the waterfowl like the terrestrial poultry. The waterfowl itself is not only a library of influenza viruses, but also a susceptible host of influenza viruses.
An acquired immune system of the fowl consists of bursal derived immunity and thymus derived immunity. Antibodies are produced through the stimulation of antigens, and three types of antibodies are produced through the cellular immune response: IgM, IgY and IgA. Li Ning team finds that the number of immune-related genes of ducklings is equal to that of immune-related genes of chickens, both obviously less than the number of immune-related genes of mammals, but the number of β-defensin genes and butyrophilin-like repertoires genes of the ducklings is obviously greater than that of the chickens. Since the poultry differs from the waterfowl in characteristics of immune response, the increasing speed and the titer of antibodies of ducklings immunized with avian influent inactivated vaccines are obviously lower than those of the chicken immunized with same. For example, after the chickens are immunized with the avian influenza inactivated vaccine, the antibody titer can reach 3 to 5 Log2, 5 to 8 Log2 and 8 to 10 log2 respectively on 7th day, 14th days and 21st days, and the antibody titer is highest on 28th to 35th days; however, after the ducklings are immunized with the avian influenza inactivated vaccine, the antibody titer can reach 2 to 3 Log2, 3 to 6 Log2 and 5 to 8 Log2 respectively on 7th day, 14th day and 21st day, and the highest antibody titer of 6 to 9 Log2 can be achieved on 28th to 35th days and can be maintained for 2 to 3 months.
Although there is a difference in the reports about the law of growth and decline for maternal antibodies of the ducklings, generally the titer of the avian influenza maternal antibodies of the ducklings is decreased from 8 to 10 Log2 for the ducklings at the age of one day to a titer less than a critical point (4 to 6 Log2) for the ducklings at the age of 7 to 9 days, and to 0 to 2 Log2 for the ducklings at the age of 15 to 28 days. The maternal antibodies may interfere with the immune effect of the avian influenza inactivated vaccine on the ducklings and even may produce immuno-suppression seriously. Since the breeding ducklings generally have relatively high avian influenza antibodies, the produced ducklings essentially have relatively high maternal antibodies which generally may protect the ducklings at the age of 1 to 15 days and may help the ducklings to resist the infection of the high-pathogenicity avian influenza viruses. When the ducklings at the age of more days receive the avian influenza immunization, the immune dead time is excessively long, which may increase the risk of the ducklings infected with the high-pathogenicity avian influenza viruses. Therefore, the ducklings may be generally immunized with the avian influenza inactivated vaccine at the age about 10 days. Since the antibodies are slowly produced after the ducklings are immunized with the avian influenza inactivated vaccine, the ducklings immunized with the avian influenza vaccine have an immune dead time about two weeks. During this period of time, the avian influenza valence is low, and the ducklings are susceptible to the avian influenza infection, resulting in serious economic loss. How to technically enable the ducklings immunized with the avian influenza vaccine to quickly produce antibodies and maintain the antibody level has an important significance on the duck farming industry.